RBW's adventures in tiny Industrial machines. Prazi lathe and milling machine score.

[Winegrower]

I can see having a mini-lathe on the bench just to avoid messing up an existing setup. But it would have to be a quality one like yours.

Edit: It's a mini-lathe, but not really mini-dollars.

 

[RaisedByWolves]

I can see having a mini-lathe on the bench just to avoid messing up an existing setup. But it would have to be a quality one like yours.

Edit: It's a mini-lathe, but not really mini-dollars.

Im not really in too deep out of pocket as I got really lucky with this deal.

After selling off much of the surplus tooling and the small lathe, Im up $290 on my initial $750 outlay. Of course I've spent probably $1500 between the lathe and the mill, but again, probably only 50% of that was out of pocket. Still have quite a bit of things to sell.


OK, all back together now and working nicely.

This is what I had been using for a feed engagement handle, not very confidence inspiring and not very positive engagement with that spindly 4mm screw and hand me down handle. It worked, but it made the engagement feel like playing with a poorly made toy vs a small machine tool.





Oh, I got a new mat for the bench to help with oil splatter and to keep things tidy and from sliding around.

The clutch engagement requires you to lift up on the handle then throw the lever. I wanted something not only beefier, but that would also have more support where it interfaces with the clutch dog engagement.....thing, the vertical part. This mechanism is functional, but simplistic and bit cheesy.

The diameter of this part is 1.028", so I took a piece of 5/8" O-1 tool steel and milled the end to a .500 radius with a 1" endmill, then turned it down to the approximate diameter of the 4mm cap screw head, did a little compound radius detail to make it look nice and Viola, a real handle stem.





This will get a turned brass cap like the tail stock handles and the rest of the handwheel stems.

Oh, did I mention I'm making new rotating handwheel stems and handles? The factory ones are just pins and don't feel very nice in your hand while operating the machine, so I made these to accept rotating brass handles also.





I'm working on a Nickel plating setup for these so they wont rust when the machine sits idle, kind of a little side quest in this adventure. I still have to work the bugs out of that process, but it will be a nice touch when its all said and done.

Here is the feed handle installed on the part I cant come up with a name for. The .028 interference between the two diameters really locks them together with a kind of spring action and this now feels solid and with the changes to the clutch dog it is now a joy to use and smooth as silk.





The bottom of the new handle overlaps the base of the pivot so Ill have to address that as it rubs a bit.

Now, looking forward I found something that will make a really nice improvement. This is the same basic lathe design but made in Bulgaria? Romania?, something like that. It has a totally different type of "Big boy Lathe" type of engagement lever I would like to make. I really like the look and this would give an even nicer more positive feel to the feed clutch.






Yes the gear train is incomplete, but this example is from someone's collection and the parts are just different enough for them to not want to install Prazi/Hobbymat/Prazimat parts even though they would work.

This ZZM "Sliven" (Yuk, what a name) is fairly rare as they were made right at the end of the cold war and economics took the production of this machine down before many were made. This also had the slow speed kit included standard where as mine had it as an option.

Slow speed kit.

The kit is cheap enough to add, but I want to go with a servo motor and driver setup that is a more common upgrade on the small lathes. These kits provide you with full torque at extremely low speeds and cost about the same as the slow speed kit, so why not go for infinite speeds at the touch of a button, even if it entails much more work to make it fit.

Got a package from the Chinese today, but that will have to wait until tomorrow.

This is going to be a real nice addition.

 

[RaisedByWolves]

The China package was a tiny OXA tool post and holders to make tool changes less of a PITA and it works perfectly.





I removed the compound for rigidity, not sure this was necessary but making a custom plinth for the tool post to sit on elevated an issue of mis matched tool post bolt and compound thread I had. You can see the 3/16" tool bit under the tool holder here and yeah, I miscalculated when making it a bit as I was making the plinth while the tool post and holders were enroute. Going to need a do over on that one. Not terrible, it just lessened the adjustability of most of the holders to accommodate a tangential (I like tan genitals) tool holder you can see in the next pic and was a mistake made via tunnel vision as I really like the versatility of that tool.


Its in the back of the lineup here and a bit out of focus.





Ill probably pick up a couple more tool holders as their only $13 each and then I can have everything mounted and ready to use when needed.

After getting that working it was time to focus my attention to mounting the ER32 collet chuck I got with this package. This included needing to make a backplate to fit it, and buying a backplate to copy. I found one for a 4 jaw chuck and bought that and copied same, and the fit on the spindle came out perfect which amazed me as I left .0015 on the inner diameter for fitting at home while making it at work.

Miraculously it fits so well that any slight tilt to it when installing locks it up tight, but it spins like its on rollers once in place and square.

Here I'm taking it down to the proper size and tediously fitting it to the collet chuck. Normally I wouldn't spend this much time on mounting a chuck (That's a lie), but being its a collet chuck I was going for broke.




Did I mention this was tedious? A small cut netted me peach fuzz. Don't forget, that is a tiny tool bit.




All done! Finish looks sketchy, but the flash picks up every microscopic detail.






And the fit I got for the chuck was easily as good as I got for the backplate to the spindle.

Here it is installed.







Now I got ahead of myself here. In order to make the backplate I needed a carriage stop so I could accurately form the shoulder the chuck mounts to. You can see half of in in the above pic. Only half because the completed stop was too long to get the tool bit as close to the headstock as needed to make the back plate.

Worked fine in any case, just wasn't micrometer settable like I wanted. It needs to be mounted to a rectangular bar that runs the length of the bed which protects the lead screw, so I had to be inventive and think outside the box on this one. I came up with a stop that with the turn of one thumbscrew (4-40 thread for added clamping force) clamps down in 4 directions equally around the bar.

Here it is disassembled so you can see the details.








And assembled so you can see how it functions. The side plates are .020 thinner than the body and .010 shorter to the center of the dovetails. This allows it to float freely when unclamped, yet be rigidly and squarely fixed in place with only moderate screw pressure. A genius effort on my part if I do say so.





And in place in its home. Its not finished yet, needs to be prettied up and some small details finalized, but I wanted to keep moving on the upgrades and will save that for when there's a lull in the work, like next time I'm out of cash for new additions and need something to do.

The micrometer body and dial was scavenged from an old tool cutter/grinder and is the icing on the cake.

Small at 1" on the thumb wheel, 3/4" on the on the micrometer dial and 5/8" on the barrel/body allowing the whole works to be around 1" in width and 1.5" length. Its tight under the chuck so everything has to be as small as possible and the 1" thumb screw knob and 4-40 screw allow ample clamping pressure with just finger tip (And that's all there is room for) pressure.







Once the fit of the chuck was finalized I added in some 3/8" holes around the perimeter for using tommy bars to help tighten the collets and indicated it. Once it checked out I marked position with punch marks on the chuck, back plate and spindle to assure accuracy when mounting it up.



I chucked up a random piece of drill rod and set up the indicator and Initially got .0015 runout and was not a happy camper.....AT ALL! Then I retraced my steps and remembered this piece was a little gritchy going into the collet, removed it and found a burr on the end I had in the collet. Turned it and hit ti with a file and cleaned up the surface with some 400 grit paper and was much more satisfied with the result.

This now proved to be a huge success as I got less than .0005 runout, but my video wont upload for some reason. I'm going to have to work on that or retake it.

Kinda bummed about that.



ETA: FIXT it! Format issue.

 

[PeterDRG]

Loving it ! I might try for the 4-way dog clutch on mine. There are lots of other things you can make, eg. a rear tool post.
30 years ago, these were very popular and there were all sorts of articles on them. As you say, they were cheap because the GDR needed hard currency, but they were excellent value. Given that everything had to come from the GDR, things like the switches weren't great, but anything engineeringwise was well made.
Cheers
Peter

 

[Pachyderm]

Fantastic thread, Wolves! I am giving it its own direct bookmark so I can look in without having to locate it. Once I get my beater SD300 in good shape I will post a thread about it. I will photograph and document as I go and then write it all up in one go. I am doing this with my Unimat SL, too. (Another great little machine!)

Thanks for the education, sir. Keep this stuff coming!

 

[RaisedByWolves]

Fantastic thread, Wolves! I am giving it its own direct bookmark so I can look in without having to locate it. Once I get my beater SD300 in good shape I will post a thread about it. I will photograph and document as I go and then write it all up in one go. I am doing this with my Unimat SL, too. (Another great little machine!)

Thanks for the education, sir. Keep this stuff coming!

Good to see you made it over here, good site with lots of helpful people.

Your best bet, if I may is to go through and document your build like I have here. This will benefit you in several ways, but the biggest help is with people encouraging you along the way. Plus you may get burnt out or life might get in the way going at it in one shot.

These machines do have some quirks as evidenced by your broken tailstock, so learn, ask advise, take your time and above all be careful with the forcing screw. That is how your tailstock got broke, too much turning of screws with out knowing the principals of operation ov the machine.

It absolutely does not help that different forcing/clamping screw arraignments and functions were used over the years either, but if you're careful you will be OK.

 

[woodchucker]

what are those two holders, the rh and lh ? and what kind of hss is that. Looks like a V

 

[RaisedByWolves]

what are those two holders, the rh and lh ? and what kind of hss is that. Looks like a V
View attachment 456639

Those are Edelstaal L&R hand tool holders. Its a really nice tooling system with most of the proper angles built right into the forged tool bit.

I have the complete set shown in 5/16" and 1/4" with a bunch of tool bits, but replacement bits are extremely expensive. They have a vague X shape that forms the cutting edge and chip breaker, and also seats them into the matching profile in the holder on the bottom.

IIRC I have close to 30 HSS bits, 10 or so of the Cobalt bits and about a dozen carbide bits, so Im good for a while. Still Im always looking out for reasonably priced replacements.

Its a shame there out of production, I think they would do well if reintroduced today.

 

[woodchucker]

they look pretty cool for hss. I like that they hold the toolbits in the orientation so you don't have to swing your tool post.

 

[woodchucker]

just found some impressive stuff... first Edelstaal tooling was made in Tenafly NJ..

Second, they made big stuff too.

40" X 120" EDELSTAAL GAP BED ENGINE LATHE: YODER #59735 | eBay

YODER MACHINERY SALES. SWING IN GAP. . DISTANCE BETWEEN CENTERS. 120". We load for free. S hipping rates available! SPINDLE HOLE. . MODEL. . SMA 1000 X 5000.

www.ebay.com